Our overall research purpose is to define the chemosensory mechanisms operating in two related brain stem functions, namely, in the control of respiration and of vomiting. Specific problems to be investigated in chemorespiratory regulation are: (1) role of cerebrospinal fluid (CSF) acid-base composition, (2) location of the central chemoreceptors, (3) interplay of chemogenic and neurogenic factors in breathing pattern generation, and (4) central drug actions in systemic intoxications. Specific problems for study in vomiting of chemical origin are: (1) modes of entry into the central emetic chemosensor (ara postrema) from the blood and CSF, (2) identification of afferent and efferent neural connections of the area postrema, and (3) kinetic assessment of agonist-antagonist drug interactions from direct recordings of vomiting behavior. Experiments in cats will incorporate measurement of vital physiological variables, perfusion of the CSF spaces, stereotaxic technique for access to deep brain structures, electrophysiological methods for stimulation of and recording from system components, histological verification of lesions and identification of tracer substances, and sterile operative procedures for chronic preparations.